INTRODUCTION
L ITHIUM - ION BATTERY IN ESS
In addition, ESS is available to each application due to its own storage mechanism, such as response time and duration. In the case of anode, carbonaceous materials are introduced and commercialized only at the early stage of LIB, such as graphite and hard carbon.
A NODE MATERIAL FOR LIB
In addition, various applications such as composites, doping, coatings and morphological control can be combined. Li2O itself can be an active material when the operating voltage is significantly extended, alloyed with transition metals such as MnO40.
S ILICON AS AN ANODE MATERIAL
It is well known that the thick SEI layer forms on the Si surface after cycling due to chemical instability. To ensure electrolyte stability and electrical conductivity, the method of carbon coating on the Si surface is generally used.
R EFERENCE
Ryu, J.; Hong, D.; Choi, S.; Park, S., Synthesis of ultrathin Si nanosheets from natural clays for lithium-ion battery anodes. C.; Park, O.; Chun, M.-J.; Choi, N.-S.; Park, S., Synthesis of microassembled Si/titanium silicide nanotube anodes for high-performance lithium-ion batteries.
A SILOXANE -INCORPORATED COPOLYMER AS AN INSITU CROSS-
I NTRODUCTION
However, electrode cracking and consequent pulverization occurs after several cycles due to the glassy nature of the electrode in which PAA is used as a binder. The one-dimensional structure and the secondary interactions of the binder are sensitive to the severe volume expansion of Si.
E XPERIMENTAL
The film was first kept under vacuum at room temperature to evaporate the solvent for 24 hours, and then cross-linked in a high-temperature vacuum oven at 250 0C for 2 hours. Schematic representation of a superior polymeric binder, TBA-TEVS-21, which is incorporated with siloxanes and cross-linked functional moieties in situ.
R ESULTS AND DISCUSSION
The high durability of TBA-TEVS-21 indicates that it can maintain electron and ion transport pathways at the silicon-silicon interface without serious side reactions. We then compared the electrochemical performance of TBA-TEVS-21 with the most commonly used so-called conventional binders such as PAA, CMC, alginate, PAA-CMC mixture and PVdF. For a deeper evaluation of the stability of the electrodes, after 100 cycles, SEM images were obtained for the electrode with TBA-TEVS-21 binder.
We analyzed the influence of the mechanical properties of the TBA-TEVS-n binder series on the electrochemical behavior (ESI, Fig. S6). The better electrochemical performance of TBA-TEVS-21 can also be attributed to its high modulus of elasticity (GPa) compared to the conventional PAA binder (GPa). The C 1s spectra showed a significantly lower intensity for TBA-TEVS-21, indicating a uniform coating of TBA-TEVS-21 on the surface of the silicon nanoparticles.
These observations represent the formation of a stable and thin layer of SEI for the electrode with the TBA-TEVS-21 binder.
C ONCLUSION
R EFERENCE
S.; Cho, J., A highly cross-linked polymer binder for high-performance silicon negative electrodes in lithium-ion batteries. Lestriez, B.; Bahri, S.; Sandu, I.; Roue, L.; Guyomard, D., On the bonding mechanism of CMC in Si negative electrodes for Li-ion batteries. S.; Yang, W.; Liu, G., Side-chain conducting and phase-separated polymeric binders for high-performance silicon anodes in lithium-ion batteries.
Guo, J.; Wang, C., A polymer scaffold binder structure for high-capacity silicon anode of lithium-ion battery. L.; Tang, D.; Yu, Z.; Regula, M.; Wang, D., Interpenetrated Gel Polymer Binder for High Performance Silicon Anodes in Lithium Ion Batteries. Xu, C.; Lindgren, F.; Philippe, B.; Gorgoi, M.; Björefors, F.; Edström, K.; Gustafsson, T., Improved Performance of the Silicon Anode for Li-Ion Batteries: Understanding ating.
An effective coupling of nanostructured Si and gel polymer electrolytes for high-performance lithium-ion battery anodes.
AN EFFECTIVE COUP LING OF NANOSTRUCTURED SI AND GEL POLYMER
- I NTRODUCTION
- E XPERIMENTAL
- R ESULTS AND DISCUSSION
- C ONCLUSION
- R EFERENCE
The thermal cross-linking reaction of GPE was investigated using an FT-IR spectrometer (FT-3000, Excalibur) with a spectral resolution of 4 cm -1 . Before the combination of the mesoporous silicon with the GPE, the physicochemical properties of the GPE were characterized. The temperature-dependent ionic conductivity of GPE is compared with that of the liquid electrolyte containing no ETPTA polymer.
In addition, the electrochemical stability window of the GPE was investigated by analyzing the cyclic voltammetry (Fig. 3-2d). The potential application of the GPE to the mesoporous silicon anode was investigated in terms of cell performance. The relatively poorer capacity retention of the GPE (4 wt% ETPTA) can be attributed to its lower ionic conductivity (Fig. 3-2c).
This result demonstrates the beneficial effect of GPE on the long-term electrochemical performance of the microporous silicon anode.
EFFECTIVE STRATEGIES FOR IMPROVING THE ELECTROCHEMICAL
- I NTRODUCTION
- E XPERIMENTAL
- R ESULTS AND DISCUSSION
- C ONCLUSION
- R EFERENCE
Effective strategies for improving the electrochemical properties of highly porous Si foam anodes in lithium-ion batteries. First, we synthesize a hierarchical Si foam structure via a magnesiothermal reduction of micrometer-sized SiO2 foam particles obtained by controlling the calcination process. The electrochemical properties of the Si foam anode were tested by galvanostatic discharge (lithiation) and charging (delithiation) in coin-type half-cells (2016 R-type).
Furthermore, we characterized surface area and pore volume of three carbon-coated Si foam particles (no calcination-Si (ncSi), air-calcined-Si (acSi), and oxygen-calcined-Si (ocSi)) (ESI, Figure S3) and S4) . During the chemical reduction process, a significant aggregation of Ag nanoparticles inside Si foam was seen due to the exothermic heat. However, the larger Ag particles were still well dispersed in the Si foam particles (Figure 5-5b).
The third strategy is to introduce metal nanoparticles into Si foam particles during the chemical reduction reaction.
MESOPOROUS SILICON HOLLOW NANOCUBES DERIVED FROM
I NTRODUCTION
More importantly, the labeled crystallographic planes of MOFs can control the deposition of ionic or molecular species without changing the initial shape. 28 Among the classical examples of MOFs, the zeolitic imidazolate framework with a metal-nitrogen coordination bond (i.e., ZIF-8) is used as an ideal template due to its exceptional chemical and thermal stability.29 In addition, the outer surface of ZIF-8 is hydrophilic due to the N-H functional groups that uniformly adhere to the precursor on the ZIF-8 surface and generate hydrolyzed oligomers as a solution-based chemical reaction.30. Here, we demonstrate the synthesis of m-Si HCs via the magnesium thermal reduction (MRR) reaction of silica-coated ZIF-8. MRR is a simple route to prepare porous Si structures along with MgO by-products.31
In this system, silica-coated ZIF-8 is converted to mesoporous silicon-coated ZnO/MgO during MRR. The MOF is used as a sacrificial template to create inner voids in the final product. The resulting m-Si HCs have several advantages: i) the architecture with the mesoporous external shell and internal void (~60 nm) can effectively accommodate a large volume expansion, 15.32 ii) the thin Si shell (thickness of ~ 15 nm) can significantly reduce the electronic and ionic diffusion pathways between electrolytes and Li-ions,15 iii) the high porosity of the Si shell can facilitate the penetration of electrolytes during electrochemical tests,33 iv) the cubic architecture improves the m-Si HC/electrolyte contact area due to the accessible exposed active face,34 which improves the diffusion efficiency.
E XPERIMENTAL
Then, these samples were leached with 1.0 M HCl for 1 h to remove MgO, followed by washing with ethanol and DI water and drying at 80 °C overnight. The morphological studies were performed with high-resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) with an acceleration voltage of 200 kV, and EDX scanning was used to characterize the elements of the samples (JEM-2100F, JEOL). Surface analysis of samples was investigated by X-ray photoelectron spectroscopy (K-alpha, ThermoFisher) with a beam of monochromatized aluminum X-ray source.
Raman spectroscopy was performed on a Confocal Raman (alpha 300R, WITec) with a laser wavelength of 532 nm. Lithium metal was used as the counter and reference electrodes, while the working electrode was composed of 70 wt% active materials, 15 wt% poly(acrylic acid)/sodium carboxymethylcellulose (CMC) (1/1 by weight) and 15 wt%. wt% of super-P representing 1.0 mg cm-2 loading density. For the full-cell test, anode was made with natural graphite/m-Si HC (90:10 in weight fraction) and consisted of active material, styrene butadiene rubber/CMC, super-P in the weight ratio while cathode (area density) = 2.9 mA h cm-2) was prepared with commercialized LiCoO2 (92 wt%), polyvinylidene fluoride binder (3 wt%) and super-P (5 wt%).
Electrochemical impedance spectroscopy (EIS) was performed in the range from 100 kHz to 0.1 Hz with an amplitude of 10 mV using an Ivium stat (Ivium Technologies).
R ESULTS AND DISCUSSION
However, additional peaks for the Si HC sample indicate the formation of MgxSiOy resulting from incomplete reduction (marked with ♣, JCPDS #34-0189). X-ray photoelectron spectroscopy (XPS) was used to elucidate the differences in the bonding characteristics of Si HC and m-Si HC. The initial voltage profiles of the cathode LCO and graphite/m-Si HC are presented in Figure S19.
After 300 cycles, the electrode thickness variation of m-Si HC (volume expansion of ~47%, Figures 6-5a and b) was less than half the value of the reference Si (volume expansion of ~107%, Figures 6- 5c) and d). Top-view SEM analysis also revealed a clear difference between the m-Si HC and reference Si (Figure S20). After 300 cycles, the m-Si HC showed low volume expansion, and the shape of each nanoparticle was maintained with the help of the voids.
Core-level XPS spectra of m-Si HC for (a) C 1s before (bottom) and after (top) cycling and (b) F 1s before (bottom) and after (top) cycling.
CONCLUSION
Depending on the size of the template used, the lateral length of Si 2D can be controlled for the appropriate range of active materials (<20 μm). As synthesized 2D has a flat film morphology (thickness in nanometers and length/width in micrometers) with negligible pores (Fig. 1h) and amorphous structure. The micro-scaled lateral dimension of 2D Si contributes to the low surface-to-volume ratio, unlike other nanomaterials.
This also explains the slightly lower specific capacitance of coated 2D Si compared to the bare specimen, as shown in Fig. Comparison between 2D Si@C (ad) and bare 2D Si (df) by the chemomechanical modeling and in situ EIS analysis during the first lithiation/delithiation. A group of the lithium concentration of (a) 2D Si@C, (f) bare 2D Si and the first principle stress of (b) 2D Si@C, (g) bare 2D Si and in situ EIS results of (c) 2D Si@C, (e) bare 2D Si during lithiation and delithiation process. d) The change in dimensional figures versus SOC calculated from the modeling.
The normalized stress of 2D Si@C is down-standardized compared to bare 2D Si due to the kinetics and structural difference.
MECHANICAL MISMAT CH-DRIVEN STRUCTURAL DEFORMATION IN SI/C
- INTRODUCTION
- EXPERIMENTAL
- RESULTS AND DISCUSSION
- CONCLUSION
- REFERENCE
